The ink jet recording method has rapidly developed and is spreading even now for the reasons that the materials are inexpensive, high speed recording is possible, the noise in the time of recording is low, and color recording is easy.
The ink jet recording method includes a continuous system of continuously ejecting ink droplets, and an on-demand system of ejecting ink droplets according to image data signals, and the ejection system includes a system of ejecting ink droplets by the application of pressure with piezo elements, a system of ejecting ink droplets by generating foams in the ink by heat, a system of using ultrasonic waves, and a system of sucking and ejecting ink droplets by electrostatic force.
As the ink jet recording ink, aqueous ink, oil ink or solid (melting type) ink is used.
The colorants for use in these ink jet recording inks are required to have good solubility or dispersibility in a solvent, to be excellent in a color developing property, to show good hue, to be fast to light, heat and active gases in the environment (oxidizing gases, e.g., NOx, ozone, etc., and SOx, etc.), to be excellent in fastness to water and chemicals, to be good in fixing ability to image-receiving materials and to hardly blot, to be excellent in preservability as ink, to be non-toxic, to be highly pure, and to be available inexpensively. However, it is extremely difficult to find colorants that satisfy these requirements on a high level. In particular, colorants for black ink having good black tone, capable of high density printing, and fast to light, humidity and heat are strongly desired.
Disazo dyes or trisazo dyes have been used as coloring matters for black, but these dyes alone are insufficient for absorption of blue and green lights and good black tone cannot be obtained in many cases, so that dyes for color correction of absorbing blue and green lights are generally used in combination. As such dyes for color correction, the dyes as disclosed in JP-A-9-255906 and Japanese Patent 3178200 are proposed to contrive the adjusting ability of black tone, a color developing property, fastness, the preservation stability of ink, water tightness, and clogging of nozzles.
However, proposed dyes for color correction in the related art are too short in wavelength of absorption, and so they are wanting in the adjusting ability of black tone such that dyes must be added in quantities or other dyes for color correction are further necessary.
Dyes capable of absorbing blue and green lights generally known are inferior in fastness and the hue is largely changed by the exposure of an image to light, heat and active gases in the environment, and the fixing ability is also insufficient. As a result, a phenomenon that the contour part bleeds with the dyes in yellow inevitably occurs under high humidity condition, thus further improvement is necessary.
In consideration of these drawbacks, a black ink composition comprising a black dye having been blended with, as the dye for color correction, a triazine dye having an absorption maximum of the absorption spectrum in the visible region at the wavelength of 435 nm in an aqueous solvent is disclosed in JP-A-2002-332426.
However, general black dyes have an absorption maximum in the wavelengths of from 570 to 620 nm, so that, considering the relationship of complementary colors important for black tone adjustment, it is apparent that suitable black tone cannot be obtained even the dye for color correction is used (Shikisai Kagaku Handbook (Handbook of Color Science), the Second Edition, pp. 560-562, Publishing Association, The University of Tokyo (1998)).
On the other hand, particularly in the ink jet recording method, a problem of a bronzing phenomenon is known in the case where a recorded image having high optical density is formed, which is a phenomenon that the crystal of the coloring matter precipitates on the surface of the recording material with the progress of drying, and the recorded image reflects light and emits metallic luster.
The bronzing phenomenon is liable to occur by the reduction of water solubility of the dye and the introduction of a hydrogen-bonding group into the dye structure for the purpose of the improvement of light fastness and gas resistance (ozone resistance). Since light is reflected and scattered by the occurrence of the bronzing phenomenon, not only the optical density of an image lowers but also the hue of a recorded image is greatly different from the desired one and the transparency is lost, so that the compatibility of the inhibition of the bronzing phenomenon and the improvement of ozone resistance is desired.
As a method of improving the bronzing phenomenon, JP-A-6-25575 and JP-A-8-337745 disclose a method of using a urea derivative and a titanium compound, but the method is still for the improvement of the bronzing phenomenon and cannot achieve the compatibility of the inhibition of the bronzing phenomenon and the improvement of ozone resistance.
Further, as a method of improving gas resistance (ozone resistance), e.g., JP-A-2003-138185 discloses a method of the addition of a specific compound to improve gas resistance (ozone resistance), but the method is still insufficient for the improvement of gas resistance (ozone resistance).